Field of the Invention
The present invention relates to an illumination apparatus suitable for image projection apparatuses and others.
Description of the Related Art
Illumination optical systems used for image projection apparatuses such as liquid crystal projectors are required to have high light utilization efficiency and to be compact. Japanese Patent Laid-Open No. 8-304739 discloses an illumination optical system in which an integrator optical system forms multiple secondary light source images and a polarization conversion element that separates polarized light is disposed near a position where the secondary light source images are formed.
In conventional illumination optical systems, an illumination area is set to be larger than a liquid crystal element, in order to allow a displacement of the illumination area due to aberration, that is, an illumination margin area is provided. In order to increase the light utilization efficiency, the illumination margin area is desirable to be reduced.
However, the illumination optical system disclosed in Japanese Patent Laid-Open No. 8-304739 generates large chromatic aberration (especially, chromatic aberration of magnification) in the integrator optical system and therefore needs to increase the illumination margin area. This results in an increase of a light amount not used for the illumination of the liquid crystal panel, which decreases the light utilization efficiency.